The aim of this study was to determine habitat suitability for juvenile freshwater pearl mussel development in Vltava River basin (Sumava National Park, Czech Republic). Bioindication experiments based on in situ exposition were performed. Both standard Buddensiek mesh cages with individual containment and sandy cages with at least 100 juveniles were used. Growth rate and survival rate were tested using juveniles of 1+ years of age. In two seasons 2014 and 2015, ten localities were evaluated including one comparative locality in neighboring Blanice River. Suitable conditions for juvenile mussel development were confirmed at several localities, as well as some unsuitable sites. A survival rate of the juveniles ranged from 0% to 100% depending on a locality position. A growth rate reached up to 153 % per 3 months exposition in the best locality. The influence of locality position within the longitudinal river profile was detected and each bioindication method gave somewhat different results. In the sandy cages, the growth rate was maximal in the middle stretch of the river. On the other hand, the growth rate increased continually downstream if evaluated by the mesh cages method which eliminates some negative environmental factors.

RS17 – Presentation

Managing multiple stress for multiple benefits: First outcomes of the EU project MARS

Water management requires solid understanding of how multiple stressors affect ecosystem state and services. By the end of 2017, the EU project MARS (Managing Aquatic ecosystems and water Resources under multiple Stress) will have concluded four years of in-depth research on this topic. MARS looked into multi-stressor responses from experimental water body to pan-European scale, developed tools for modeling and diagnosing multi-stressor effects and guided management of multiply stressed aquatic ecosystems. Our presentation summarizes the project’s progress, and provides first outcomes and key messages.

Burbot is one of the most mysterious freshwater species, typically inhabiting cold and oligotrophic waters, therefore it is highly sensitive to anthropogenic changes (e.g., euthrophication, global warming) and hence protected in many areas. Monitoring of burbot populations is difficult because of rare catch in commonly used nets. Therefore we developed a unique sampling scheme using considerate methods (visual exploration by SCUBA divers, two types of fyke nets, electrofishing) and long-lines simulating anglers practice. This scheme was tested in four Czech drinking-water reservoirs with burbot stocking for biomanipulative purposes to control planktivore species. Efficiency of the sampling methods was dependent on local conditions. Burbots were captured in three reservoirs. Young burbots were captured in the inflowing streams or in littoral zone of reservoirs with rubbles. Bigger burbots inhabited deeper parts of reservoirs. A subsample of burbots was analysed in laboratory to determine length, weight, age and stomach content. Most of the burbots were young (up to 3 years old) and the age groups corresponded to stocked fish. The preferred food items were ephemeral insects, fish and permanent water invertebrates. The other food sources were zooplankton, terrestrial insects and crayfish. Our study is unique in complex conception, starting in development of sampling procedure and ending in discussion of burbot ecology.

This study was supported by grant of the Czech Science Foundation (15-01625S), by the University of South Bohemia (158/2016/P) and by the Norwegian Financial Mechanism 2009-2014 under contract number MSMT-28477/2014 (7F14316).

RS10 – Presentation

How much can environmental DNA (eDNA) reflect a local macroinvertebrate community in a lotic system?

Recent developments in the use of molecular techniques for bio-assessment has led to a revolution in the way we can monitor aquatic systems. Current methods of monitoring macroinvertebrates in freshwater rely heavily on the capture or sighting of the target species, followed by correct taxonomic identification, which is not always possible. This is particularly true when referring to invasive alien species (IAS) which can be cryptic, in low density or in juvenile stages. This makes eDNA a particularly interesting complimentary tool when assessing macroinvertebrate communities and as an early warning system for new IAS. However, little is known about how molecular methods compare to established methods in lotic systems. Here we demonstrate the findings of a series of field experiments comparing established sampling techniques (kick samples) with molecular samples, namely - DNA “smoothies”, eDNA water and eDNA sediment samples.

RS08 – Presentation

River restoration scheme to improve migratory pathways for potamodromous cyprinids

Sabor River a tributary of the Douro River (N. Portugal) was one of the last wild Iberian rivers. Sabor hydropower dam was recently constructed, blocking fish migration immediately at the river mouth. As a compensation measure the downstream segment of Vilariça R., an impacted tributary running parallel to main stream, was elected for restoration to replace some of the lost areas. The aim was to create spawning grounds and to improve the migratory pathways for the potamodromous cyprinids from Douro River, especially Luciobarbus bocagei. Water from the Sabor reservoir was derived in a submerged channel to the lower Vilariça R. to increase the water flow, but it was necessary to define the most appropriate volume of water to be released. Restoration included also: submerged weirs with fish ramps to increase the lotic/ lentic sequence, lunkers, bank reinforcement, and river water profile increase. Field work took place during the spawning season. To build the 1D model, 45 river-bed profiles were taken, as well as hydraulic measurements (i.e. velocity and depth) at 6 cross-sections. The CASiMiR Fish model together with the 1D Hec-RAS was used to calculate the Weighted Usable Area (WUA) in the spawning season considering the river morphology after the restoration scheme. Fuzzy sets and rules for two life-stages of the Iberian Barbel were defined based on expert knowledge and fish surveys. This study allowed to define the minimum flow to promote and maintain the spawning grounds and also the efficiency of the integrate rehabilitation.

Microbial respiration (R) is a major contributor to carbon dioxide (CO2) emissions from freshwaters. Herein, terrestrial dissolved organic matter (DOM) is one of the main substrates for R, whereby its availability is linked to its molecular composition, i.e. quality. Future hydrological changes will likely alter both quantity and quality of DOM exported from terrestrial sources to freshwaters. However, a controversy exists on the importance of DOM quality in the microbial mediated carbon cycle in these systems. This study aimed to (i) understand how two specific terrestrial DOM sources with distinct qualities and different mixtures (mixed in different proportions) influence R, and (ii) explore driving factors of R. We performed a short-term incubation experiment, mixing two terrestrial substrates of contrasting 13C isotopy and quality at different proportions but the same concentration to a natural microbial community inoculum. The substrates were a highly available (labile) isotopically labelled beech leaf leachate (DOMleaf) and a refractory peat leachate (DOMpeat). During the experiment, we measured R intensity and isotopic signature (d13C), dissolved nutrients, and DOM quality characteristics. We observed a strong treatment-effect on R, while the quantity of emitted CO2 significantly increased with increasing proportion of labile DOM (DOMleaf). Thereby, isotope analysis showed that the observed stimulation in R was dominated by decomposition of DOMleaf. The DOM quality characteristic molecular weight was the strongest predictor of R. Our results suggest a tight linkage between R and DOM quality, indicating that labile terrestrial DOM likely supports high levels of R and consequently CO2 emissions of freshwaters.

Due to deterioration in previous decades the ecological river water quality reached an absolute minimum during the 1990ies in many European rivers. Large and small rivers suffered from hydromorphological degradation and were characterized by a poor chemical water quality. This facilitated the loss of key species and promoted a general loss of biodiversity in Europe’s freshwater ecosystems. Since the enforcement of the European Water Framework Directive in 2000, the ecological water quality has drastically increased, allowing the recolonization and restoration of freshwater biota. Clear and robust guidelines are needed to obtain cost-efficient solutions in river management. Habitat suitability models have proven to be useful to support decision making in river management. In this study, we developed species distribution models, based on habitat preference curves, to define the biological response of a species (presence/absence) to abiotic gradients. This allowed us to indicate the conditions and locations which are suitable for the (re-)introduction of brown trout, a rheophilic fish species, in the Zwalm river basin (Belgium). Based on an ensemble approach, we found that temperature, stream velocity and pool/riffle pattern are the most important variables determining the occurrence of the species. By linking the outcome of our models to the actual water quality conditions of the river basin, we are able to pinpoint the most suitable locations for the reintroduction of brown trout. Our results show that using such a modelling approach is valuable to support reintroduction programs in the Zwalm river basin or other river basins in Europe.

SS08 – Presentation

Monitoring invasive crayfish using environmental DNA (eDNA): a lab and field evaluation

Environmental DNA (eDNA) techniques are becoming increasingly popular in conservation and invasion biology, especially for monitoring and early detection of rare, endangered or invasive species. An exponential increase in divergent methods regarding eDNA collection and analysis has been observed, which leads to mixed success in detection efficiency in studies on aquatic invertebrates. In this study, we tested and compared three DNA extraction methods using crayfish as model species. Based on existing and newly developed primers we were able to identify two invasive crayfish species (Procambarus clarkii and Orconectes limosus) from tissue and filtered eDNA samples from water of aquaria kept in the laboratory as well as water from natural ponds. Both species could be positively identified in field and laboratory samples, though effectiveness differed greatly. Results in our study seemed to be highly dependent on primer choice, DNA extraction method, chosen species, and the type of sample (tissue or filter). Our results showed that the MasterPure extraction kit consistently provided the most reliable results for tissue and for filtered eDNA samples for both species. The results are promising, but also highlight the necessity for a standardized protocol for each step of the eDNA process.

RS09 – Poster

Exploring the potential use of hydro-drones for freshwater mussels survey

Long-term monitoring of freshwater taxa is usually hampered by expensive and time-consuming visual surveys. This is the case of freshwater mussels that are rapidly declining due to ecosystem alterations worldwide. Important basic information on them (distribution, habitat preferences, ecophysiological constraints) are scarce. Unfortunately, the possibility to acquire this basic information is impeded by inadequate funding. Exacerbating this problem is the difficulty to track and observe freshwater mussels, because they are often rare and clustered. In addition, mussel surveys are often hampered by restrictive environmental conditions. Although the choice of an appropriate sampling design can improve the likelihood that a survey meets its goals, there is no sampling design that can correct an access problem. To escape this bottleneck we started exploring the potential use of hydro-drones, developed for this purpose by a recently created start-up company. Hydro-drones are regarded as beneficial tools for obtaining data that cannot be accessed otherwise. However, to date their use for research, monitoring and protection of species surprisingly still not consider them.
A pilot project, assessing the efficiency of hydro-drones and their application limits under gradients of environmental constraints, was developed to survey mussels in the recently recolonized Lake Orta.

RS08 – Presentation

Colonisation of the restored stream by benthic invertebrates: a case study from the Bohemian Forest (Czech Republic)

In the Czech Republic, the vast majority of stream restoration projects have been focused on technical improvement of the channel morphology of small streams and their in-stream habitat enhancement. They have included mostly re-meandering of streams, construction of small impoundments, and sediment removal from backwaters and impoundments on streams to improve stream hydrology and water retention in the floodplain. Biological responses to restoration, however, are rarely monitored or evaluated methodically and the post-project evaluation of implementation of the primary restoration goals is lacking.
Our monitoring survey is focused on the restoration of the lower stretch of the mountain stream Hučina in the Bohemian Forest (Šumava NP) which was returned to its original meandering course by complete restoration of its channel. Simultaneously, its modified channel and drainage channels in the floodplain were blocked or buried. The long-term monitoring focused on both benthic invertebrates and in-stream habitat development began immediately after the restoration in November 2014. Our results of two-year monitoring after the restoration show surprisingly rapid colonisation of invertebrates, though the conditions are not yet favourable for some species. Remarkably species-rich and numerous communities of invertebrates were found shortly after the restoration and fish and lampreys were observed repeatedly. Due to unstable (fine) bottom substrate, however, benthic invertebrates are vulnerable to high water discharge after spates and further development of their communities will be related on the bottom substrate conditions.